EF184 SE Project

[dorrisant]

Hey guys,

I have a couple handfuls of EF184 tubes on my bench just waiting for a project. Got a good Mullard and Amperex Bugle Boy among others.

I also have a decent old chassis that will work as well... two noval sockets, two octals (rect and power tube), a dinky PT (47mA) and a 5k primary SE OT that was used with a 6v6 at some point... it came to me with a 6k6. I also have the rect tube and 6e5 indicator tube from the original device....

I'm thinking of sticking with the 6v6, although I saw a schematic somewhere that had a choice of plugging in a 6v6 or smaller octal or unplug it and plug in an EL84... can anyone tell me where to find that schem?

My question is... do any of you guys have any suggestions or schematics? There are two preamp sockets... so there are quite a few ways to approach it. I want to put it together as a test bed for some mods... maybe the EF184 as one input stage into a 12xxx and use the other 12xxx triode as a second input.

What do you think?

I will buy new transformers for the cause if needed.

Thanks in advance!
Tony

[dorrisant]

I did leave out something...

Reasons for trying these tubes:

The EF184 can be subbed for the EF86.
I don't know exactly what the differences are, but I would love to find out. I am not going to quote a number at the risk of stupidity, but the gain is a lot higher in the EF184. I have read that it is a bit creamier as well. Maybe this is a little less known than I thought.

They are relatively CHEAP and there are some great brands available to anyone who puts a slight effort into it.
I bought 9 wonderful NOS EF184s (Mullard, Bugle Boy, Tung Sol, etc.) for $19.99... w/free shipping! I would question the integrity of just one EF86 you could buy for that price!

So I'm kinda looking for a schematic... relatively simple, single ended, EF86 based pre with the idea of tweaking values to get the EFF184 happy, or angry whichever sounds better.

Maybe Tom could redo the title... "EF86 to EF184 conversion SE Project".... ?

Any ideas?
Tony

[overtone]

I did leave out something...

Reasons for trying these tubes:

The EF184 can be subbed for the EF86.
I don't know exactly what the differences are, but I would love to find out.

You noticed the different pin-out right?

Under the roof I have a box of fifty of those EF184s which I picked up in London a while back to try exactly your idea out. I think it was 14 quid the lot.
The plan was to try a simple AC15 circuit EF184 >PI>6V6 in pp.

In the meantime I had some fun with other small pentodes 6SJ7, EF86, 5879, by varying the voltages of the plate and screen and different cap values by-passing screens.
The vox values and voltages are not gospel, but it seems that the g2 wants to be roughly around 1/3rd of Plate voltage.
Merlin has a great chapter on the small pentodes in his preamp book.

Thanks for the post, it reminded me to get that "test" going soon.

Best, tony

[dorrisant]

You noticed the different pin-out right?

The vox values and voltages are not gospel, but it seems that the g2 wants to be roughly around 1/3rd of Plate voltage.
Merlin has a great chapter on the small pentodes in his preamp book.

Yes, but only after looking at the data sheets...

Reading Merlin's preamp book chapter 3 right now...

I hope to hear your findings!

Tony